1. Field of the Invention
The present invention relates to improved flame retardant insulation compositions for wire and cable products. More specifically, the insulation compositions of the invention exhibit improved abrasion resistance and are comprised of a bimodal high density silane-containing polyethylene base resin formulated with a flame retardant compound and silanol condensation catalyst.
2. Description of the Prior Art
In addition to having good processability and flame retardance automotive wire and cable compositions must also have and retain over their service life certain physical characteristics. One physical property which has become increasingly important in recent years, due to ever more stringent service requirements, is abrasion resistance. Even though currently available compositions may satisfy the requirements of SAE J1128 which utilizes a sandpaper abrasion test, these same compositions may fail to meet the abrasion requirements of ISO 6722, Section 9.2. This latter specification has been adopted by most European car manufactures and utilizes a much more demanding needle abrasion test.
For example, crosslinkable flame retardant ethylene-vinylacetate (EVA) copolymer insulation compositions are disclosed in U.S. Pat. No. 5,439,965. The compositions, obtained by formulating EVA copolymers of specified vinyl acetate contents with halogenated compounds, antimony trioxide and organic peroxide, have improved sandpaper abrasion resistance (determined in accordance with ASTM D 3389); however, they will not meet the more stringent requirements of ISO 6722, Section 9.2.
Crosslinkable silane polymer compositions are also used for wire and cable insulation. Silane polymers used for this technology can be obtained by grafting unsaturated alkoxysilanes to ethylene polymers as described in U.S. Pat. No. 3,646,155 or by copolymerizing ethylene with an unsaturated alkoxysilane as described in U.S. Pat. Nos. 3,225,018 and 3,392,156. Filled moisture curable silane copolymer compositions of the latter type are disclosed in U.S. Pat. Nos. 5,266,627 and 5,312,861.
It would be highly useful if moisture curable silane-based insulation compositions having improved abrasion resistance were available. It would be even more advantageous if the silane-based compositions met the needle abrasion resistance requirements of ISO 6722, Section 9.2. These and other objectives are achieved with the improved compositions of the invention.